very simple - verwundet means that the injury was the result of enemy action whereas verletzt was the result of an accident, a crash landing etc.

You will find IV./JG 1 in JFV 10/II, p 50 - it started the year as IV./JG 1 and was renamed I./JG 1 as of April 1st, 1943. It is therefore as usual dealt with under the designation it had at the end of the year.